(Field of the Invention)
The present invention relates to a steer-by-wire steering device configured to perform steering by use of a steering wheel which is mechanically unconnected with a shaft between tie rods, the shaft being for performing turning. In particular, the present invention relates to a control device for a steer-by-wire steering mechanism configured to perform toe angle control, in a steer-by-wire steering device including a toe angle control mechanism.
(Description of Related Art)
A toe angle of wheels of a vehicle at the time of shipment from a factory is set in consideration of traveling stability. However, such a setting of the toe angle is not a setting that realizes optimum fuel efficiency. For example, when the toe angle is set to be toe-in, due to a rearward component of lateral force acting on the wheels, travel resistance increases and the fuel efficiency decreases.
There has been proposed a method for improving the fuel efficiency by controlling alignment of wheels such as the toe angle in accordance with a traveling state (for example, Patent Document 1). However, in order to control the toe angle in accordance with a traveling state, as disclosed in Patent Document 1 above, the toe angles of the left and right wheels need to be controlled independently of each other. Therefore, for example, when the steering mechanism of the vehicle is connected to the left and right wheels, the toe angle cannot be changed.
As another technology for improving the fuel efficiency, there has been proposed a technology in which the toe angle is set to “0” during accelerating or constant-speed travel, to improve the fuel efficiency of the vehicle traveling straight, and a toe angle in a toe-in direction is provided during decelerating travel, to ensure the vehicle stability (for example, Patent Document 2).
As a method for determining wheel alignment that realizes the best fuel efficiency, there has been proposed a method in which wheel alignment that makes the speed decreasing rate lowest when the vehicle is traveling straight in a state no braking and driving force is being generated is determined as wheel alignment appropriate for the vehicle traveling straight (for example, Patent Document 3). As still another technology for improving the fuel efficiency, there has been proposed a method in which the fuel efficiency is calculated from a fuel injection amount and a travel distance, and wheel alignment that realizes the best fuel efficiency is stored (for example, Patent Document 4).